Bypass type coriolis effect flowmeter

ABSTRACT

A bypass flowmeter for measuring the material flow in a conduit. An optimum pressure drop is developed across the flowmeter by coupling the material outlet of the flowmeter to the throat of a venturi positioned within the conduit. This increased pressure drop improves the material flow rate through the flowmeter. This enhances flowmeter accuracy and sensitivity and the flowmeter&#39;s ability to measure mass flow rates for low density materials such as gas. The ratio of the material flow within the flowmeter to that of the conduit is derived with improved precision over prior arrangements which assume a constant ratio of material flow between the flowmeter and the conduit. The material flow information for the conduit is obtained for materials having a varying viscosity by the use of a differential pressure sensor which measures the pressure drop across the flowmeter and transmits this information to instrumentation which uses it to derive material flow information for the conduit with improved precision. An alternative embodiment not having a venturi operates in the same manner to derive the material flow ratio between the flowmeter and the conduit and, in turn, the total material flow in the conduit.

RELATED APPLICATIONS

This application is a continuation in part of U.S. application Ser. No.08/587,550 filed 17 Jan. 1996 , now abandoned, and whose disclosure ishereby incorporated by reference to the same extent as if fully setforth herein.

FIELD OF INVENTION

This invention relates to a Coriolis effect mass flowmeter and moreparticularly, to a Coriolis effect mass flowmeter of the bypass typethat is coupled to a conduit for measuring and deriving informationpertaining to material flow in the conduit.

PROBLEM

Coriolis effect mass flowmeters measure mass flow and other informationfor materials flowing through a conduit. Such flowmeters are disclosedin U.S. Pat. Nos. 4,109,524 of Aug. 29, 1978,4,491,025 of Jan. 1,1985,and Re. 31,450 of Feb. 11,1982, all to J. E. Smith et al. Theseflowmeters have one or more flow tubes of straight or curvedconfiguration. Information regarding the characteristics of materialflowing in a Coriolis mass flowmeter must be derived with great accuracysince it is often a requirement that the derived flow rate informationhave an error of less than 0.15% of reading. These flowmeter outputsignals are sinusoidal and are displaced in time or phase by an amountdetermined by the Coriolis forces generated by the flowmeter throughwhich the material flows. The signal processing circuitry which receivesthese sensor output signals measures this time difference with precisionand generates the desired characteristics of the flowing processmaterial to the required error of less than 0.15% of reading.

Coriolis mass flowmeters may be operated on a full flow or bypass basis.They are generally operated on a full flow basis in applications whereinthe diameter of the conduit whose material flow is to be measured issufficiently small so that a commercially available mass Coriolisflowmeter can be used to receive the entire material flow in theconduit.

The currently available Coriolis mass flowmeters are not capable ofoperating on a full flow basis with conduits having a diameter ofgreater than 6 inches or about 150 mm. However, it is often necessary tomeasure material flow in conduits whose diameter is greater than that ofthe commercially available Coriolis full flowmeters. In theseapplications, the material flow may occasionally be measured on a bypassbasis by a volumetric flowmeter coupled to the conduit so that some ofthe material flow in the conduit is diverted to flow through a bypassflowmeter while the remainder of the material flows through the conduit.The volumetric flowmeter measures the material flow within its bypasschannel and outputs its inferred information regarding the material flowwithin the conduit. A problem associated with the use of the volumetricbypass flowmeters is that the ratio of the flow through the meter tothat through the conduit can vary with fluid properties, includingdensity, velocity, and viscosity. Since volumetric meters do not measureall of these properties, they are unable to compensate for variation inthe flow ratio. Thus the inferred total flow rate is likely to be inerror.

Another problem with volumetric bypass flowmeters is that they requirethe mass flow rate to be calculated from the material density which isnot measured by these meters but is determined from calculations usingtemperature, pressure, and material characteristics. A Coriolisflowmeter offers greater accuracy, and the ability to measure mass flowdirectly. Their use is therefore preferred over that of volumetricflowmeters.

Although the currently available Coriolis flowmeters are satisfactoryfor full flow applications, their output information is not sufficientfor bypass applications requiring comparable accuracy. Their mainproblem is that, like volumetric bypass meters, the ratio of thematerial flow through the flowmeter to that through the conduit oftenvaries with the material density, velocity, and viscosity. Thisvariation causes inaccuracies in the flow calculation derived for theconduit.

The prior art, such as U.S. Pat. No. 5,333,496, has ignored thesepossible inaccuracies and has assumed a constant material flow ratiobetween the bypass flowmeter and the conduit. This constant ratio isbased upon the cross sectional area of the flowmeter tube and the crosssectional area of the conduit whose material flow is to be measured. Theuse of a constant material flow ratio may be acceptable for use withapplications wherein high accuracy is of no concern or wherein actualflow ratio variations are held to a minimum with the use of materialhaving a constant density, viscosity, and flow rate. However, theassumption of a constant ratio is not acceptable in applications wherehigh accuracy information for material flow within the conduit isdesired. This is particularly the case when measuring conduit flow formaterials whose density and/or viscosity is not constant.

The typical Coriolis mass flowmeter can provide output informationregarding the mass flow rate and volumetric flow rate of the materialwithin it. It can also provide output information regarding the densityof the flowing material. The density information is derived from theresonant frequency of the flowmeter flow tubes. U.S. Pat. No. 5,359,881to Kalotay et al., discloses a Coriolis flowmeter having an internaldifferential pressure sensor that permits the flowmeter and itsassociated electronics to provide viscosity information as well asdensity, mass flow rate, and volumetric flow rate for the materialflowing within it. Thus, the Kalotay et al., flowmeter, when operated asa bypass flowmeter coupled to a large conduit, would eliminate some ofthe problems associated with the calculation of the material flow ratiobetween the flowmeter and the conduit by generating output informationfor the variable parameters of material density and viscosity. However,Kalotay discloses only the flowmeter structure per se including adifferential pressure sensor that permits a viscosity calculation.Kalotay does not teach how the output information of his meter could beused to determine the ratio of material flow within his flowmeter tothat of a conduit to which his flowmeter might be connected on a bypassbasis.

Another problem with the use of Coriolis flowmeters on a bypass basis isthat they require a relatively large pressure differential between theirinlet and outlet in order to operate in their most accurate flow range.In current bypass flowmeters, this is achieved by an orifice plate orventuri located in the conduit between the meter inlet and the meteroutlet. The orifice plate or venturi create a pressure drop which drivesmaterial through the flowmeter. The problem with an orifice plate isthat the pressure is permanently lost from the system.

It can be seen that the traditional use of Coriolis (and volumetric)bypass flowmeters, wherein the flow ratio is assumed to be constant,creates problems which cause them to generate output information that isnot always as accurate as is required in certain installations.Furthermore, it can be seen that the use of orifice plates to generateenough pressure drop for Coriolis meters to operate in their mostaccurate flow range is undesirable because of energy loss.

SOLUTION

The present invention overcomes the above identified problems andachieves an advance in the art by providing a Coriolis bypass flowmetersystem whose total pressure drop in a connected conduit is lower thanthat produced by either a Coriolis meter or an orifice plate.Furthermore, the present invention's derived material flow outputinformation is of greater accuracy than that heretofore available.

The Coriolis bypass flowmeters of the present invention overcome theproblems associated with the use of orifice plates within a conduit togenerate sufficient material flow through the flowmeter. They overcomethese problems by the use of a venturi (a converging/diverging nozzlestructure) positioned within the interior of the conduit. A materialinlet to the flowmeter is positioned upstream (or downstream) of theventuri and a material outlet of the Coriolis bypass flowmeter ispositioned at the throat of the venturi. This generates a sizeablepressure drop between the inlet and outlet of the Coriolis bypassflowmeter and, in turn, generates an increased material flow through theCoriolis bypass flowmeter.

Having a high material flow rate through the Coriolis flowmeter reducesmeasurement error in two ways. The first is due to the fact that much ofthe error in a standard Coriolis meter (such as meter zero error) isindependent of flow rate. For instance a flowmeter might have anuncertainty in the flow rate of one pound per minute. At a flow rate of10 pounds per minute this can amount to a ten percent error. At a flowrate of 1000 pounds per minute this amounts to only a one tenth of onepercent error.

The second way that a high flow rate through the Coriolis flowmeterreduces error has to do with the flow ratio. If the base uncertainty inthe flow rate of the Coriolis flowmeter is once again one pound perminute and the flow ratio is one thousand to one, then the uncertaintyin the flow through the conduit is one thousand pounds per minute. Onthe other hand, if the ratio is fifty to one, then the uncertainty inthe flow through the conduit is only fifty pounds per minute. The bypassmeter's sensitivity to flow is effectively increased by increasing theportion of flow that goes through the Coriolis meter. Thus it becomesobvious that it is desirable to have a high material flow rate throughthe Coriolis flowmeter.

The problems caused by a net pressure drop in the conduit of the priorart orifice plate bypass flowmeters does not occur in the use of thebypass flowmeter of the present invention. This results from the factthat the present invention uses a venturi to generate a pressuredifferential, such that the pressure is recovered downstream of thethroat of the venturi. The positioning of the material outlet of thebypass flowmeter at the throat of the venturi results in a largepressure differential between the material inlet and outlet of theflowmeter. This differential generates a sizeable material flow throughthe flowmeter that provides increased flowmeter sensitivity andaccuracy. Downstream of the throat of the venturi, the bulk of thepressure is restored to the material in the conduit system. The use ofthe venturi to generate this pressure differential and, in turn, theincreased material flow through the flowmeter is preferable to that ofthe use of orifice plates and the like whose resulting materialturbulence results in lost energy.

The present invention determines the total material flow within theconduit in a new and novel manner. Fluid dynamic equations are derivedand show that the flow ratio between the flowmeter and the conduit is afunction of the fluid properties and the meter flow rate. The Coriolismeter (along with a differential pressure gage, when necessary) is thenused to determine the relevant material properties. The metermicroprocessor in an associated electronics element can then be used tocalculate the flow velocity in the venturi and the total conduit massflow rate.

The relevant material properties, as previously discussed, are density,velocity, and viscosity. The Coriolis meter determines the density ofthe material from the resonant frequency of the vibrating tubes of theflowmeter. It measures the mass flow rate within the meter and from thisinformation along with density and flow tube cross sectional area, itthen derives the velocity of the material flow. Pressure drop across themeter is determined with a differential pressure sensor connectedbetween the material inlet and outlet of the flowmeter. The differentialpressure provided by the sensor is used to derive the viscosity of thematerial.

The fluid velocity in the venturi is determined by using the materialproperty values output by the Coriolis meter to solve the appropriatefluid dynamic equation 25 subsequently disclosed herein. Informationregarding material flow velocities in the conduit and flowmeter istranslated to volumetric flow rates and to mass flow rates usingpre-programmed internal dimensions of the flowmeter and conduit alongwith the continuously measured material density. The mass flow ratewithin the flowmeter is added to the mass flow rate within the venturiin order to derive the entirety of the mass flow rate within the conduitdownstream of the venturi. Thus, the bypass flowmeters of the presentinvention overcome the problems associated with the use of volumetricbypass flowmeters by operating in such a manner that they continuouslymeasure density and automatically generate output information in termsof either mass or volumetric material flow.

In summary, the generation of an increased flowmeter pressuredifferential and, in turn, an increased material flow provides aCoriolis bypass flowmeter of increased sensitivity and accuracy thatcompensates for variations in density and, velocity, and viscosity bydirectly measuring these parameters.

DESCRIPTION OF THE DRAWINGS

The above and other advantages of the invention can be better understoodfrom the reading of the following detailed description thereof taken inconjunction with the drawing in which:

FIG. 1 discloses a vertical cross-section view of a Coriolis flowmeterconnected on a bypass basis to a conduit having a venturi affixed to theinner walls of the conduit.

FIG. 2 discloses a vertical cross-section view of a Coriolis flowmetercoupled on a bypass basis to a conduit having an internal venturistructure positioned intermediate to the inner walls of the conduit.

FIG. 3 is a cross-section end view of the structure of FIG. 2.

FIG. 4 discloses a Coriolis bypass flowmeter of the insertion typepositioned within the confines of a conduit with the downstream portionof the flowmeter comprising a venturi structure.

FIG. 5 is a cross-section end view of the structure of FIG. 4.

FIG. 6 discloses an alternative arrangement similar to that of FIG. 1except that material inlet 106 is positioned downstream of materialoutlet 111.

FIG. 7 discloses an arrangement similar to that of FIG. 4 except that apair of separate pressor sensors 435A and 435B are positioned at theends of tubes 432 and 433.

FIG. 8 discloses an alternative to that of FIG. 1 wherein a venturi isnot present inside the conduit.

FIG. 9 is a flow chart of the processing steps utilized in the presentinvention.

DETAILED DESCRIPTION

Description of FIG. 1

FIG. 1 discloses a conduit 101 in which material flows from an upstreamend 102 to a downstream end 103. A Coriolis flowmeter 104 having aninlet 106 and an outlet 107 is coupled to conduit 101 in order tomeasure a portion of the material flow in the conduit to deriveinformation pertaining to the entirety of the material flow within theconduit.

The material inlet 106 is positioned within the interior of conduit 101with the open end of the material inlet 106 facing upstream. Thisdiverts a portion of the material flow into the interior of the materialinlet 106. The material that enters inlet 106 flows through Coriolisflowmeter 104 and exits the Coriolis flowmeter 104 at its materialoutlet 107 which has an opening 111 which is proximate the surface 112of element 108. Element 108 is affixed to the inner surface 113 ofconduit 101. Element 108 forms a venturi having a throat area T.

It can be seen that the opening 111 of outlet 107 is positionedproximate throat T of the venturi. The coupling of material inlet 106and material outlet 107 of Coriolis flowmeter 104 to conduit 101 permitsCoriolis flowmeter 104 to be subjected to an optimum pressure drop. Thispressure drop increases the material flow through the Coriolisflowmeter. This increased pressure drop is attained by the positioningof material outlet 111 proximate the throat of the venturi so as to takeadvantage of the low pressure generated at the venturi throat T ascompared to the material pressure at inlet 106 of Coriolis flowmeter104.

FIG. 1 also discloses a differential pressure gauge 134 connected bymeans of tubes 132 and 133 to material inlet 106 and material outlet 107of flowmeter 104. These connections enable the differential pressuregauge 134 to provide a continuous monitoring of the material pressuredrop developed across flowmeter 104. Differential pressure gauge 134transmits this differential pressure information over path 115 to meterelectronics 114 which derives a continuous indication of the viscosityof the material flowing through flowmeter 104. As subsequently describedin connection with the embodiment of FIG. 4, meter electronics applies adrive signal over path 116 to oscillate the flowmeter tubes and receivessignals over path 117 to derive information pertaining to the materialflow in flowmeter 104 including the volumetric and mass flow rate of thematerial. As subsequently described in detail, the meter electronicselement 114 uses the measured density information, measured mass flowrate, the measured pressure drop as well as other information includingthe parameters of the conduit and the flowmeter to derive the ratio ofthe material flow rate of the flowmeter and the venturi and in turn, themass flow rate and volumetric flow rate of the entirety of the materialflowing within the interior of conduit 101.

FIG. 2 discloses an alternative embodiment to that of FIG. 1 whereinlike numbers represent the elements of FIG. 2 that directly correspondto similarly designated elements of FIG. 1. The primary differencebetween the two embodiments is that the embodiment of FIG. 1 has aventuri formed by elements 108 affixed to the inner wall 113 of conduit101 while in the embodiment of FIG. 2, the venturi comprises a separateventuri element 208 positioned within the interior of the conduit 101.Venturi 208 is held in a fixed position within the conduit 101 by meansof support brackets 211 and 212 as shown in FIG. 3.

It has been previously mentioned that it is a problem when using bypasstype flowmeters to determine the ratio of the material flow through theflowmeter compared to the material flow through the conduit since theratio varies with changes in material density and velocity. The presentinvention solves this problem since Coriolis type flowmeters measuredensity and can calculate velocity. This allows for the calculation ofthe flow ratio and thus compensates for changes in material density andvelocity.

The embodiment of FIGS. 2 and 3 also includes differential pressuresensor 134 together with conductors/paths 115, 116 and 117 which enablemeter electronics 114 to operate in the manner described in connectionwith FIG. 1 to derive the mass flow rate and volumetric flow rateinformation for the entirety of the material flow within conduit 101.

As is subsequently described, the differential pressure sensor 134 isnot necessary for applications in which the viscosity of the materialflow in conduit 101 is a constant. In this case, the differentialpressure sensor 134 is not required and the remainder of the disclosedapparatus operates as described to derive flow rate information forconduit 101. However, for applications wherein the material in conduit101 is not of a constant viscosity, the use of a differential pressuresensor enables meter electronics 114 to derive fluid viscosity. Knowingviscosity allows the determination of the conduit flow rate withimproved precision. The differential pressure sensor 134 of FIGS. 1, 2and 3 need not be an external device as shown in connection with FIG. 1,2 and 3, but instead may, if desired, be internal to the flowmeter asshown in connection with the embodiment of FIG. 4.

Viscosity can be determined through use of a differential pressure gageto measure the pressure difference between the inlet and outlet of theCoriolis meter. Pressure difference is a function of flow rate andviscosity. Since pressure drop and flow rate are measured, viscosity canbe determined as per U.S. Pat. No. 5,359,881.

Calculation of Venturi Material Flow Velocity

The following mathematical derivation shows the dependence of the flowratio between the flowmeter and the conduit upon velocity(flow rate),density, and viscosity. It also shows how the venturi velocity and thetotal flow rate of the flowmeter and the conduit may be calculated oncethese fluid parameters are known.

The flow through the bypass flowmeter 104 of FIGS. 1 and 2 is driven bythe pressure differential developed at the throat T of venturi 108. Inorder to understand how a venturi works it is necessary to understandthe components of pressure in flowing material. The first component isstatic pressure, and is the pressure with which we are most familiar. Itis the pressure of static material in conduit 101. Moving material alsohas a static pressure. It is measured by facing a pressure sampling tubeperpendicular to the material flow direction in conduit 101.

The second component is dynamic pressure. It is the kinetic energy of aflowing material and can be measured as the difference in pressurereadings from a tube facing upstream and a tube facing perpendicular tothe material flow direction. Dynamic pressure is calculated from theequation: ##EQU1## The total material pressure, TP, in conduit 101 isthe sum of the dynamic and static pressures. ##EQU2##

Neglecting viscous pressure drop, the total pressure TP in venturi 108is conserved by Bernoullis' law and is equal to that at the upstream endof the conduit at location A. Some of the static pressure Ps isconverted to dynamic pressure Pd in throat T and then back to staticpressure downstream of venturi 108. A venturi accomplishes this functionby the decreased area at throat area T. The decreased area at throat Tforces the material velocity to increase, so that the dynamic pressurePd increases while the static pressure Ps decreases. Downstream of thethroat, the conduit area again increases, the material velocity anddynamic pressure decrease, and the static pressure increases. A properlydesigned venturi can accomplish these conversions with very little dropin total pressure TP.

The material flow in the present invention is driven by the differencebetween the static pressure Ps at the inlet B which is upstream ofventuri throat T and the static pressure Ps at the flowmeter outlet 111.

The total pressure in the upstream portion of conduit 101 at point A isgiven by the equation: ##EQU3## The static pressure in the inlet 106 toflowmeter 104, position B, is equal to the total pressure at A (which byBernoullis' law is equal to the total pressure at B) minus the dynamicpressure due to the material velocity through the flowmeter. Forsimplicity in this derivation, it will be assumed that the flowmetertube, the inlet 106, and the outlet 107 are all of the same diameter andthus all contain material of the same velocity. ##EQU4## Substitutingequation 3 into equation 4 yields: ##EQU5##

The static pressure in the outlet 111 of flowmeter 104 is equal to thestatic pressure in venturi throat T which is equal to the total pressureTP_(A) minus the dynamic pressure Pd in throat T. This is true sinceTP_(A) =TP_(t). ##EQU6## Substituting equation 3 into equation 7 yields:##EQU7## Simplifying equation 8 one gets: ##EQU8##

The difference in static pressure between the inlet and outlet offlowmeter 104 is then given by the equation: ##EQU9## Substitutingequations 6 and 9 into equation 10 yields: ##EQU10## Simplifyingequation 11 one gets: ##EQU11## Thus, neglecting viscous losses in theventuri, it can be seen that the pressure that drives material throughthe bypass flowmeter 104 is proportional to the difference in velocitysquared of material in flowmeter 104 and the venturi throat T. Bydecreasing the throat area the driving pressure can be increased so thatthe bypass flowmeter operates in its optimum flow range. The overallpressure drop in the conduit 101 is minimal because of the conversion ofthe dynamic pressure back to static pressure downstream of the venturi.

The pressure differential driving the material through the bypass meteris given by equation 12. In order to determine the ratio of the flowthrough flowmeter 104 to that through the venturi 108 it is alsonecessary to know the resistance to flow or viscous pressure dropthrough both the flowmeter and the venturi. The equations of resistanceto flow through a pipe are dependent on the flow regime (laminar orturbulent) which is a function of the Reynolds number of the material.The Reynolds number is a dimensionless number which is used tocharacterize flow. The Reynolds number is given by the equation:##EQU12##

A Reynolds number of 2000 to 3000 is generally recognized as theapproximate transition zone between laminar and turbulent flow. Sincethis zone is extended (not an exact point), and since the pressure dropequation for turbulent flow is different than for laminar, an ambiguityexists as to which pressure drop equation (laminar or turbulent) isappropriate. This ambiguity requires the flowmeter of the new inventionto be operated at flow rates entirely in the turbulent regime.Fortunately, the use of the venturi to drive the flowmeter flow makesthis feasible.

The pressure drop for flow through a pipe is given by the Darcy formula.##EQU13## The Darcy formula is of generic enough form that it is usedfor different flow regimes (laminar or turbulent), geometries (straightor bent), and surface finishes (smooth or rough). The only difference inthe formula for these different conditions is in the friction factor.The friction factor for turbulent flow in smooth straight pipes up to aReynolds number of about 10⁵ is given by the Blasius equation. ##EQU14##

The friction factor, f_(b), for a ninety degree bend in a pipe (as inthe bypass flowmeter of FIG. 1 ) is a constant times the friction factorfor a straight pipe. ##EQU15## n=constant (function of bend radiusdivided by tube diameter The bypass meter of FIG. 1 has several bendsand several straight sections. Since the bend friction factor andstraight tube friction factors are of the same form, they can becombined into a single term friction factor for the bypass flowmeter ofFIG. 1. This single term is equation 15 multiplied by a constant##EQU16## Thus the pressure drop through the meter can be represented bythe equation: ##EQU17##

The viscous loss in the venturi between the flowmeter inlet and outletcan also be represented by the Darcy formula if one uses arepresentative diameter and velocity. The proper velocity forcalculating viscous pressure drop in the venturi is a fraction of thethroat velocity, cVt. ##EQU18## The Darcy formula for the venturi thenbecomes: ##EQU19##

This viscous pressure drop for the venturi is added to the venturipressure differential from equation 12. The sum is the pressure drivingthe material through the meter. ##EQU20##

The pressure drop through the meter is now set equal to the pressuredriving the flow through the meter. The ratio of material flow throughthe meter to material flow through the venturi can then be found bysolving the resulting equation for the velocity ratio.

    δP.sub.S =P.sub.drop.sbsb.m

Substituting equations 18 and 21 into equation 22 yields: ##EQU21## Thisequation can be solved for the velocity ratio between the flowmetermeter and the venturi throat. ##EQU22## Substituting equations 13 and 15into equation 23: ##EQU23##

From equation 25 it can be seen that the material velocity ratio isdependant upon not only the known meter and venturi geometric constants,but also on the material density, viscosity, and even material velocity.Traditional volumetric bypass meters can only determine the metermaterial velocity, V_(m), but without knowing the density or viscositythey cannot determine the throat velocity, or total flow with accuracy.The use of a Coriolis meter as the bypass meter allows the determinationof both material density and velocity. This leaves only viscosity andthroat velocity as unknowns. Viscosity can be dealt with in severalways. First, if the viscosity is constant and known, its value cansimply be entered into equation 25. If the viscosity is a known functionof temperature, it can be calculated using the fluid temperature asmeasured in the Coriolis meter. (Coriolis meters require the temperaturebe known in order to compensate for changes in elastic modulus withtemperature.) Finally, if viscosity varies in an unknown manner, it canbe determined through use of a differential pressure gage to measure thepressure difference between the inlet and outlet of the Coriolis meter.Pressure difference is a function of flow rate and viscosity. Sincepressure drop and flow rate are measured, viscosity can be determined asper U.S. Pat. No. 5,359,881 using the Hagen Poiseuille equation:##EQU24## The only unknown in equation 25 at this point is the velocitythrough the throat of the venturi which can be determined by iterativelysolving the equation. Once the throat velocity V_(t) is known, thethroat mass flow rate can be determined (velocity times density timesthroat area). The total conduit mass flow rate is simply the sum of theflowmeter and venturi throat mass flow rates. The calculations outlinedabove are easily and quickly performed by use of a microprocessor suchas already exists in the Micro Motion model RFT 9739 which may comprisemeter electronics 114 and which is available from Micro Motion, Inc., inBoulder, Colo. 80301. The geometry of FIG. 1 can determine conduitmaterial mass flow rate with higher precision than present bypassflowmeters by use of a standard Coriolis mass flowmeter in conjunctionwith a venturi, and, if necessary, a differential pressure gage.

The RFT 9739 (meter electronics 114) is currently programmed andoperational to derive mass flow rate, volumetric flow rate and densityinformation for the material flowing through an associated Coriolisflowmeter such as element 104 on FIG. 1. If the flowmeter is alsoequipped with a differential pressure sensor, the RFT 9739 can alsoderive material viscosity information. In accordance with the presentinvention, the RFT 9739 solves equation 25 for Vt after being programmedwith constants representing the flowmeter and conduit geometry such asLm, dm, Lv, dv, etc. It then derives the mass flow rate in the venturiand then in the entirety of the conduit. In accordance with spirit ofthe invention, the RFT 9739 can also derive conduit material mass flowrate information based upon geometries using other fluid equations.

Equation 25 was derived for the preferred embodiment in which a venturiin the conduit is used to increase the flow rate through the Coriolismeter. It can be shown through similar analysis that equation 25 also istrue for the embodiment of FIG. 8 where there is no venturi in theconduit. In this embodiment, without the venturi, the venturi length, Lvof equation 25, becomes the distance in the conduit between theflowmeter bypass inlet and outlet, the venturi diameter (dv) becomes theconduit diameter, and the venturi throat velocity (Vt) becomes theconduit fluid velocity between the flowmeter bypass inlet and outlet.

Since equation 25 also applies to non-venturi Coriolis bypassflowmeters, as well as venturi flowmeters, as shown in FIG. 8,correction can be made for variations in bypass ratio of thesenon-venturi meters resulting in improved accuracy over prior art bypassmeters. The preferred embodiment, however, contains a venturi whichfurther enhances accuracy by increasing the amount of flow through theCoriolis meter.

Description of FIG. 9

FIG. 9 is a flow chart illustrating the preceding description andequations which disclose the steps of the process by which the presentinvention derives the total mass flow rate in a conduit coupled to abypass type flowmeter.

Processing begins with element 900 and proceeds to step 902. Step 902operates to determine the mass flow rate, density and material velocitythrough the bypass flowmeter. The Coriolis bypass flowmeter measures themass flow rate and density of the material through the bypass flowmeter.This information is used, knowing the geometry of the bypass flowmeter,to derive the material velocity through the bypass flowmeter. Processingthen proceeds to step 904 of FIG. 9.

The material viscosity is determined during step 904. This step is notnecessary if the material viscosity is known or constant. As describedabove with respect to FIGS. 1-3, a differential pressure sensor is usedin conjunction with the Coriolis bypass flowmeter to determine thematerial viscosity. After determining the material viscosity, processingcontinues to step 906.

During step 906 equation 25 is solved for Vt, the throat velocity. Theother components of equation 25 include values already measured in steps902-904 and flowmeter conduit geometry constants. Equation 25 which issolved for Vt during step 906 is the same whether a venturi is used, asin FIG. 1 or not, as in FIG. 8. Processing next proceeds to step 908.

During step 908 the mass flow rate through the conduit between thebypass flowmeter inlet and outlet is calculated. The throat velocity Vt(solved for during step 906) is multiplied by the material density(measured in step 902) the product of which is multiplied by thetransverse area at the point for which the throat velocity iscalculated. Processing next proceeds to step 910.

During step 910 the material mass flow rate through the conduit betweenthe flowmeter inlet and outlet (determined during step 908) is added tothe material mass flow rate through the Coriolis bypass flowmeter(measured during step 902) to determine the total conduit mass flowrate. Once the total material mass flow rate is determined during step910, processing concludes with element 912.

Description of FIGS. 4 and 5

FIGS. 4 and 5 disclose an alternative embodiment of the inventioncomprising a bypass flowmeter 400 inserted within the interior ofconduit 101. Conduit 101 has an upstream end 102 and a downstream end103 as shown for conduit 101 on FIGS. 1 and 2. Bypass flowmeter 400 hasan upstream end with an opening 402 and body surfaces 401. Flowmeter 400further has a downstream end comprising tip 407 and body surfaces 406.Flowmeter 400 further has a middle portion comprising outer shell 404.Outer shell 404 encloses a hollow chamber 427 through which flowchannels 409 and 411 pass. Flow channel 409 includes an inlet portion412 which is connected to opening 402. Flow channel 409 further includesan outlet portion 414 connected to element 434 which has an openingflush with surface 406 proximate the throat T of the venturi. Flowchannel 411 includes an upstream inlet 413 connected to opening 402. Itfurther includes an outlet 415 connected to channel 434 having anopening flush with surface 406 proximate the throat portion T of theventuri. The hollow chamber 427 also contains driver 417 and sensors 421and 423 between flow channels 409 and 411. Brace bars 424 and 425interconnect the walls of flow tubes 411 and 409. Driver 417 comprises acoil and magnet M combination in the mid portion of hollow chamber 427.Driver 417 is energized by a drive signal received over path 115 whichvibrates the flow tubes 409 and 411 at their resonant frequency whenmaterial flows therein. Chamber 427 further includes a pair of sensors421 and 423, each comprising a coil and magnet M combination whichdetect the transverse movements of flow tubes 409 and 411 as they arevibrated at their resonant frequency by driver 417 under control of thedrive signals received on path 115. The oscillations detected by sensors421 and 423 are extended over path 116 to meter electronics 114 which,in a well known manner, determines the phase difference between thereceived signals. The phase difference between these signals isindicative of the mass flow rate of the material in flow channels 409and 411. Meter electronics 114 also determines the density of theflowing material from the frequency of the oscillations applied to path115. The meter electronics uses the mass flow and density informationtogether with pre-programmed information regarding the relativediameters of the flow channels 409 and 411 and the diameter of conduit101 to determine the mass flow rate and other desired information forthe entirety of the material flowing within the interior of conduit 101.

It should be noted that the exit opening of outlet 434 is positionedproximate the throat T of the venturi formed by surfaces 406. Thispermits the flowmeter 400 to be subjected to an optimum pressure dropbetween its outlet 434 and its inlet 402. In so doing, the flowmeter ofFIG. 4 operates in the same manner as previously described for theflowmeter 104 of FIGS. 1 and 2 to derive the desired information for theentirety for the material flowing within the interior of conduit 101.

FIG. 5 is an end view of the embodiment of FIG. 4 and illustrates a pairof struts 501 and 502 connecting the outer surface of flowmeter 400 tothe inner surface of conduit 101. Conductors 115-117 extend through thecenter of strut 501 to connect meter electronics to flowmeter 400.

Insertion Coriolis flowmeter 400 also contains a differential pressuresensor 435 which is positioned within the hollow chamber 427 and isconnected by tube 432 to upstream opening 402 and is further connectedby tube 433 whose outlet end 416 joins the material outlet 434 of theflowmeter. Differential pressure gauge 435 detects the pressuredifference between the material inlet 402 of flowmeter 400 and thematerial outlet 434 of flowmeter 400. This pressure differentialinformation is applied to meter electronics 114 over path 115 on FIG. 5which uses this pressure differential information to derive theviscosity for the flowing material.

The flowmeter 400 may be operated without the differential pressuresensor 435 in installations in which the flowing material in conduit 101has a near constant viscosity such as is the case for water, or when thematerial has a viscosity that is a known function of temperature whichis measured by the flowmeter. However, in applications in which theviscosity is unknown, the differential pressure sensor 435 can derivethe material viscosity. The viscosity information then can be used inequation 24 to derive the ratio between the velocity of the materialflow within the venturi throat to that of the flowmeter materialvelocity. Having determined the velocity within the throat and theflowmeter, the mass flow rate for the material in the throat can bederived from the following relationships: ##EQU25## This mass flow ratein the entirety of the conduit is the sum of the mass flow rate in thethroat and the mass flow rate through the Coriolis flowmeter.

Description of FIG. 6

FIG. 6 discloses a bypass Coriolis flowmeter system similar to that ofFIG. 1. The difference is that in the system of FIG. 6 the flowmeterinlet 106 is positioned downstream of outlet 111. In FIG. 6, some of thematerial in conduit 101 will flow into inlet 106, through flowmeter 104and outlet 111 back into the interior of the conduit. The material flowsin that direction since the material pressure at inlet 106 is greaterthan that at outlet 111 due to the low pressure at the throat T of theventuri.

Description of FIGS. 7 and 8

A single differential pressure sensor 435 together with tubes 432 and433 as shown on FIG. 4 is not necessary and if desired, can be replacedwith two separate pressure sensors 435A and 435B, one of which can bepositioned at the terminus of tube 432 at material inlet 402. The othercan be positioned at the terminus of tube 433 at material outlet 434.The signals from these two individual pressure gauges can then beapplied over conductors 116A and 116B to meter electronics 114 (notshown on FIG. 7) which can then operate in the same manner as describedfor FIGS. 4 and 5 for the use of a single differential pressure gauge435 to derive material viscosity. Driver 417 and sensors 421, 423 onFIG. 7 may be connected by conductors to meter electronics 114, 115 and117 in the same manner as shown on FIG. 5.

FIG. 8 discloses an embodiment similar to FIG. 1 except the interior ofconduit 101 is devoid of the venturi structure 108. Inner surface 113 ofconduit 101 is substantially flat and the material flow throughflowmeter 134 is due to the conduit pressure drop between the flowmeterinlet B and outlet 111. The principal of operation of the embodiment ofFIG. 8 is the same as that of FIG. 1.

It is to be expressly understood that the claimed invention is not to belimited to the description of the preferred embodiment, but encompassesother modifications and alterations within the scope and spirit of theinventive concept. For example, the invention has been described withreference to the use of Coriolis flowmeters 104 and 400. The inventionis not so limited and if desired, may be operated with a volumetricflowmeter as element 104 if the material density is constant. When sooperated, a volumetric flowmeter having an inlet positioned shown, orelement 106 in FIG. 1, and having an outlet positioned proximate thethroat T of a venturi may be advantageously subjected to an optimumpressure drop which will permit the flowmeter to operate in an optimummanner to determine the volume of the material flowing there through andin turn, the volume of the material flowing in the entirety of conduit101. Furthermore, the same approach may be applied to differentgeometries and flow conditions where the specific equations may differ.But the method of determining the relevant material parameters andcompensating for variations in the bypass ratio is still valid.

In summary, it is desirable to use bypass meters on large conduitsconducting high rates of material flow. Existing bypass meters, however,lack the high accuracy required of many applications because the bypassratio varies with the material parameters. The Coriolis flowmeters ofthe present invention enhance their accuracy without the penalty ofpermanent material pressure drop. This is achieved by use of a venturito increase the portion of flow that goes through the Coriolis meter.Furthermore, the fluid dynamic equations associated with a venturi basedbypass meter enable the bypass ratio to be calculated from the metergeometry and the fluid's relevant properties. The Coriolis meters of thepresent invention continuously measure the relevant material propertiesand continuously calculate the bypass ratio and total mass flow rate.

We claim:
 1. Flow measurement apparatus for measuring material flow in aconduit, said apparatus comprising:a flowmeter; a material inlet fordiverting some of said material flow in said conduit to said flowmeter,wherein said material inlet is positioned within an interior of saidconduit and coupled to said flowmeter; a material outlet for returningmaterial flowing in said flowmeter to said conduit, wherein saidmaterial outlet is positioned within said interior of said conduit andcoupled to said flowmeter; means for determining the mass flow rate andflow velocity and density of said material flow in said flowmeter; meansresponsive to said determination of said mass flow rate and said flowvelocity and density of said material flow in said flowmeter fordetermining the flow velocity and mass flow rate of said material in aportion of said conduit between said material inlet and said materialoutlet; and means responsive to said determination of said mass flowrate in said flowmeter and in said conduit portion for determining atotal mass flow rate of said material in said conduit.
 2. The apparatusof claim 1 wherein said means for determining said flow velocity andmass flow rate of said material in a portion of said conduit betweensaid material inlet and said material outlet comprises a means fordetermining the ratio of the flow velocity between said material in saidflowmeter and said material in said portion of said conduit.
 3. Theapparatus of claim 1 further comprising:means for determining theviscosity of said material in said flowmeter; means responsive to saiddetermination of said viscosity and to said determination of said flowvelocity and said mass flow rate and said density of said material insaid flowmeter for determining said flow velocity and said mass flowrate of said material in said portion of said conduit; and said meansresponsive to said determination of said flow velocity and mass flowrate of said material in said conduit portion determines said totalmaterial mass flow rate in said conduit.
 4. The apparatus of claim 3wherein said means for determining said flow velocity and mass flow rateof said material in said portion of said conduit between said materialinlet and said material outlet comprises a means for determining theratio of the flow velocity between said material in said flowmeter andsaid material in said portion of said conduit.
 5. The apparatus of claim1 wherein said flowmeter comprises a Coriolis mass flowmeter.
 6. Theapparatus of claim 5 wherein said Coriolis mass flowmeter furthercomprises:pressure sensing means coupled to said material inlet and tosaid material outlet for producing a measurement of a material pressuredrop between said material inlet and said material outlet; and meansresponsive to said measurement of said material pressure drop fordetermining the viscosity of said flowing material.
 7. The apparatus ofclaim 6 wherein said means for determining said total mass flow rate ofsaid material in said conduit comprises:said means for determining saidflow velocity and said mass flow rate of said material in said flowmeteras well as said material density and said material viscosity; and saidmeans responsive to said determination of said flow velocity, mass flowrate, density and viscosity of said material in said flowmeterdetermines said mass flow rate of said material in said portion of saidconduit between said material inlet and said material outlet.
 8. Theapparatus of claim 1 wherein said flowmeter is a volumetric flowmeter.9. The apparatus of claim 1 further comprising:means for increasing saidflow velocity of said material in said conduit at a conduit locationproximate said material outlet between said material inlet and saidmaterial outlet; said material outlet being coupled to said conduit atsaid location having an increased flow velocity of said material in saidconduit for generating an optimum pressure drop between said materialinlet and said material outlet to increase said flow velocity of saidmaterial within said flowmeter.
 10. The apparatus of claim 9 whereinsaid flowmeter comprises a Coriolis mass flowmeter.
 11. The apparatus ofclaim 10 wherein said Coriolis mass flowmeter further comprises:pressuresensing means coupled to said material inlet and to said material outletfor producing a measurement of a material pressure drop between saidmaterial inlet and said material outlet; and means responsive to saidmeasurement of said material pressure drop for determining the viscosityof said flowing material.
 12. The apparatus of claim 11 wherein saidmeans for determining said total mass flow rate of said material in saidconduit comprises:said means for determining said flow velocity and saidmass flow rate and said density as well as said viscosity of saidmaterial in said flowmeter; means responsive to said determination offlow velocity, mass flow rate, density and viscosity of said material insaid flowmeter for determining said flow velocity and mass flow rate ofsaid material in said conduit portion of increased flow velocity; andsaid means responsive to said determination of said flow velocity andmass flow rate of said material in said conduit portion determines saidtotal mass flow rate of said material in said conduit.
 13. The apparatusof claim 9 wherein said flowmeter is a Coriolis mass flowmeter;andwherein said means for determining said material flow velocity andsaid mass flow rate of said material in said portion of said conduitbetween said material inlet and said material outlet comprises a meansfor determining the ratio of the flow velocity between said material insaid flowmeter and said material in said portion of said conduit. 14.The apparatus of claim 13 wherein said Coriolis mass flowmeter furthercomprises:pressure sensing means coupled to said material inlet and saidmaterial outlet for measuring the material pressure drop between saidmaterial inlet and said material outlet; and means responsive to saidmeasurement of said material pressure drop for determining the viscosityof said flowing material.
 15. The apparatus of claim 14 wherein saidmeans for increasing said flow velocity of said material comprises aventuri positioned internal to said conduit; andwherein said materialoutlet is coupled to a throat area of said venturi.
 16. The apparatus ofclaim 13 wherein said venturi is affixed to the inner surface of saidconduit.
 17. The apparatus of claim 15 wherein said venturi and saidthroat area are spaced apart from the inner surfaces of said conduit.18. The apparatus of claim 13 wherein said Coriolis mass flowmeter ispositioned external to said conduit.
 19. The apparatus of claim 1wherein said material outlet is positioned upstream of said materialinlet in said conduit.
 20. The apparatus of claim 1 wherein saidmaterial outlet is positioned downstream of said material inlet in saidconduit.
 21. The apparatus of claim 20 wherein said Coriolis massflowmeter is positioned within said conduit.
 22. The apparatus of claim21 wherein said Coriolis mass flowmeter comprises:an elongated bodypositioned internal to said conduit with said body and said conduithaving parallel longitudinal axes; an upstream end of said body havingsaid material inlet for receiving material to be extended through saidCoriolis mass flowmeter; a downstream end portion of said body havingsaid material outlet for discharging material from said body back tosaid interior of said conduit; a pair of parallel flow channels withinsaid body having longitudinal axes parallel to said longitudinal axis ofsaid body; means coupling the downstream end portion of said flowchannels with said downstream end portion of said body; means couplingthe upstream end portion of said flow channels with said upstream endportion of said body; wherein material that enters said inlet of saidbody is extended through said flow channels and said outlet of said bodyand is returned back to said material flowing in said conduit; means forvibrating said channels transversely and longitudinally with respect toeach other; and means including sensor means coupled to said flowchannels and responsive to said vibrating while material flows throughsaid flow channels for determining said total material mass flow rate insaid conduit.
 23. The apparatus of claim 22 wherein said downstream endportion of said body comprises a venturi and wherein said outlet of saidbody is positioned proximate the throat of said venturi.
 24. Theapparatus of claim 23 wherein said Coriolis mass flowmeter furthercomprises:pressure sensing means coupled to said material inlet and saidmaterial outlet for measuring the material pressure drop between saidinlet and said outlet; means responsive to said measurement of saidmaterial pressure drop for determining the viscosity of said flowingmaterial; and means responsive to said determining of said viscosity todetermine the flow velocity and mass flow rate of said material in saidventuri and, in turn, the total mass flow rate of said material in saidconduit.
 25. A method of measuring material flow in a conduit; saidmethod comprising the steps of:diverting some of the material flow in aconduit to a flowmeter having a material inlet positioned within aninterior of said conduit and coupled to said flowmeter; returningmaterial flowing in said flowmeter to said conduit via a material outletpositioned within said interior of said conduit and coupled to saidflowmeter; determining flow velocity and mass flow rate and density ofsaid material in said flowmeter; determining flow velocity and mass flowrate of said material in a portion of said conduit between said materialinlet and said material outlet in response to said determination of flowvelocity and mass flow rate and density of said material in saidflowmeter; and determining a total mass flow rate of said material insaid conduit in response to said determination of said flow velocity andmass flow rate of said material in said flowmeter and of said materialin said conduit portion.
 26. The method of claim 25 wherein saidflowmeter comprises a Coriolis mass flowmeter.
 27. The method of claim25 including the steps of:coupling pressure sensing means to saidmaterial inlet and to said material outlet for producing a measurementof a material pressure drop between said material inlet and saidmaterial outlet; and determining the viscosity of said flowing materialin said flowmeter in response to said measurement of said materialpressure drop.
 28. The method of claim 27 including the stepsof:determining said flow velocity and said mass flow rate as well assaid density and said viscosity of said material in said flowmeter;determining the flow velocity and mass flow rate of said material insaid conduit portion in response to said determination of said flowvelocity, mass flow rate, density and viscosity of said material in saidflowmeter, and said step of determining said total mass flow rate ofsaid material in said conduit.
 29. The method of claim 25 furthercomprising the steps of:increasing said flow velocity and mass flow rateof said material at a conduit portion proximate said material outlet;and coupling said material outlet to said conduit at said locationhaving an increased flow velocity and mass flow rate for generating anoptimum pressure drop between said material inlet and said materialoutlet of said flowmeter to increase said material flow within saidflowmeter.
 30. The method of claim 29 wherein said flowmeter is aCoriolis mass flowmeter; andwherein said step of determining flowvelocity and mass flow rate of said material in said portion of saidconduit between said material inlet and said material outlet comprises astep of determining the ratio of the flow velocity between said materialin said flowmeter and said material in said portion of said conduit. 31.The method of claim 30 including the steps of:measuring a materialpressure drop between said material inlet and said material outlet; anddetermining the viscosity of said flowing material in response to saidmeasurement of said material pressure drop.
 32. The method of claim 31including the steps of:determining said flow velocity and said mass flowrate as well as said density and said viscosity of said material in saidflowmeter; determining said flow velocity and mass flow rate of saidmaterial in said conduit portion of increased flow velocity in responseto said determination of said flow velocity, mass flow rate, density andviscosity of said material in said flowmeter, and said step ofdetermining said total mass flow rate of said material in said conduitin response to said determination of said flow velocity and mass flowrate of said material in said flowmeter and of said material in saidconduit portion.
 33. The method of claim 29 including the step whereinsaid increased flow velocity is obtained by positioning said materialoutlet proximate a throat of a venturi.
 34. The method of claim 33wherein said method further comprises the steps of:operating pressuresensor means coupled to said flowmeter for measuring the materialpressure drop between said material inlet and said material outlet ofsaid flowmeter; and determining the viscosity of said material flow insaid flowmeter in response to said measurement of said material pressuredrop.
 35. The method of claim 25 including the steps of:positioning anelongated body positioned of a Coriolis mass flowmeter internal to saidconduit with said body and said conduit having parallel longitudinalaxes; extending material received by an upstream end portion of saidbody having said material inlet through said Coriolis mass flowmeter;discharging material from said body back to said interior of saidconduit via a downstream end portion of said body having said materialoutlet; a pair of parallel flow channels within said body havinglongitudinal axes parallel to said longitudinal axes of said body;connecting the downstream ends of said flow channels with saiddownstream end portion of said body; connecting the upstream endportions of said flow channels with said upstream end portion of saidbody; wherein material that enters said material inlet of said body isextended through said flow channels and said material outlet of saidbody and is returned back to said material flowing in said conduit;vibrating said flow channels transversely with respect to each other;and operating sensor means responsive to said vibrating while materialflows through said channels for determining information pertaining tosaid material flow in said conduit.
 36. The method of claim 35 includingthe steps of:positioning said material outlet of said body proximate athroat of a venturi formed by said body.
 37. The method of claim 36including the steps of:operating pressure sensor means coupled to saidbody for measuring the material pressure drop between said materialinlet and said outlet of said flowmeter body; determining the viscosityof said material flow in said flowmeter in response to said measurementof said material pressure drop; and determining said total mass flowrate of said material in said conduit in response to said viscositydetermination.